Which might mean Romulans got warp drive a century before the movie, that is, around TOS (and thus perhaps didn't have it in "Balance of Terror" yet, even though their plasma cloud weapon effortlessly moved apace with the hero starship that flew at "emergency warp"). Or just that warp drive was the decisive factor in turning Romulans into a credible empire in the 2260s, when the species first challenged the RNZ and was offered the two paths of development - but that warp drive as such was old news.

In any case, both Romulans and Cardassians were introduced as "old and neglected" enemies, presumably not powerful enough to warrant constant attention. Klingons in turn were introduced as an "ongoing" foe.